737 Probe Heat ON before start-up
Usually, the Probe Heat (or Pitot Heat for the Classic) switches are selected to ON after engine start-up. Supplementary Procedures 16 for Cold Weather Operations clearly state to put them on after the preflight procedure. Some argue that switching them on with say just 7° C and wet runway or light rain would be overkill, but these are icing conditions also according to the FCOM. Would this be too pedantic?